Stanislas Wawrinka left Great Britain's Davis Cup hopes hanging in the balance with a 6-3 7-6 (7-5) 6-4 win over Andy Murray to give Switzerland a 2-0 lead.
The Scot was bettered by the Swiss number two's aggressive strokes in the opener and lost a tight second set after going 3-0 up in the tie-break.
The players swapped breaks in a tense third but Murray's mistakes handed Wawrinka the decisive break late on.
Britain must now win the doubles on Saturday to have any hope of promotion.
Team captain Jeremy Bates' tactic of resting British number two Greg Rusedski on the opening day could now prove to be fatal to the team's hopes of getting back in the world's top 16.
Murray, in his debut Davis Cup singles match, conceded he was simply beaten by the better player
"I played pretty well for two-and-a-half sets," said the 18-year-old.
"But I didn't serve or return as well as I would have liked. I can't play my best tennis every day.
"I wouldn't say it is a blip, I've lost against a guy who's ranked 50 places higher than me in the rankings."
Wawrinka's searching groundstrokes undid Murray in the opener and he quickly broke the Scot in the fourth game.
The crowd roared on the Swiss number two in the Palexpo Arena and he broke again.
A lapse of concentration handed Murray one break back but Wawrinka recovered to wrap up the set in 41 minutes.
Murray was back on form in the second and silenced the crowd with some clever shots at the net and his pace around court.
But the 18-year-old could not break down Wawrinka and when he was ahead in the tie-break some poor selection let the Swiss back in to take a two-set lead.
Murray appeared to have rallied at the start of the third as he quickly went 2-0 up.
But the Swiss world number 60 piled on the pressure, forcing Murray into mistakes to break back.
Despite flashes of brilliant play, Murray could simply not find any consistency and it was his errors that saw Wawrinka muscle his way to a straight sets win.
The triumph on home soil was Wawrinka's first Davis Cup victory and could be decisive in restoring Switzerland to the World Group.